Bell Ringer Socrative Quiz- Newton’s Laws Room: LEE346 Sign in: Lastname,Firstname Hurry 10 minutes until quiz closes!!

Objectives We will analyze the forces acting on an object. I will draw free body diagrams and analyze the force, mass and acceleration of an object using Newton’s 2nd law, F=ma

Forces SI Unit for Force is the Newton (N) The formula for force is F = ma NOTE: the unit for mass is kg and the unit for acceleration is m/s2… so a kg•m/s2 is the same thing as a Newton!

Forces A force causes an object to change its velocity, by a change in speed OR direction Force is a vector quantity since direction is important Vectors in Opposite directions– SUBTRACT Vectors in same directions- ADD

Free-body diagrams A free body diagram shows the magnitude and direction of all forces acting on a single body, usually drawn as a box with arrows. The diagram shows the body only and the forces acting on it.

Forces and Free Body Diagrams (FBD)

Type of Force Symbol Description Frictional Ffrict force exerted between surfaces as an object moves across it Tension Ftens force transmitted through a string, rope, cable, or wire Normal Fnorm force exerted on an object when it is on top of another object; ┴ to resting plane Air Resistance Fair force exerted on object as it travels through the air; usually negligible Applied Fapp force on an object being pushed or pulled Spring Fspring force exerted by a stretched or compressed spring with an object attached to it Gravitational Fgrav force of gravity that all objects on Earth experience

Free Body Diagrams (FBD) Directions for drawing FBDs : 1. Draw the object as a box 2. The larger the force the longer the vector arrow should be 3. The direction of the in the direction that the force is acting 4. Always label your force vectors 5. With balanced forces/ constant velocity vectors are equal 6. With unbalanced forces/ acceleration/deceleration vectors are unequal

FBD Example A book on a table is being pushed to the right at a constant velocity

FBD Example A parachutist jumps out of an airplane; include air resistance

How would I draw the FBD?

How would I draw the FBD? This is what the FBD should look like!

How would I draw the FBD?

How would I draw the FBD?

How would I draw the FBD?

Examples Mass hanging on a rope T (tension in rope) W (weight)

Examples Inclined slope Force of Gravity is always straight down. The Normal force is perpendicular (90° ) to surface. Inclined slope FN (normal force) Ff (friction) Fg(weight)

Pulled / Pushed at an angle

Solving

Net force Net Force- sum of the forces acting on object in a given direction. (horizontal & vertical separately)

Net Force ? ? ?

Net Force

It’s physics, there’s always a mathematical relationship! Newton’s 2nd law There is a mathematical relationship between the net force and acceleration. net force (N) = mass (kg) x acceleration (m/s2) It’s physics, there’s always a mathematical relationship! Fnet = ma

Example What will be Mr. Porter’s acceleration? Mass of Mr Porter and bike = 100 kg Pushing force (100 N) Friction (60 N)

An example net force = 100 – 60 = 40 N moving to the left FNet = ma a = 0.4 m/s2 Mass of Mr. Porter and bike = 100 kg Applied force (100 N) Friction (60 N)

Remember Weight = Fgrav = mX a Fgrav= m X g Use g as 9.8~ 10 m/s2 Also Remember, Fnorm = Fgrav